Poly(vinylamine) has been used in many industrial and pharmaceutical applications. In the papermaking industry, poly(vinylamine) products have been used as dry and wet strength additives to improve paper and paperboard strength and as retention/drainage aids to improve paper productivity. U.S. Pat. No. 2,721,140 originally disclosed the use of poly(vinylamine) molecules as papermaking additives to improve paper wet strength. U.S. Pat. No. 4,421,602 disclosed the partially hydrolyzed polymer of poly(N-vinylformamide) for improving flocculation, fines retention and pulp drainage in papermaking. U.S. Pat. No. 6,159,340 described the use of the partially hydrolyzed poly(vinylamine) products as dry and wet strength additives for paperboard. U.S. Pat. Nos. 6,616,807 and 6,797,785 described a variety of poly(vinylamine) derivatives as drainage aids, flocculants, and retention aids for papermaking. U.S. Pat. No. 5,961,782 disclosed the use of poly(vinylamine) to make crosslinkable creping adhesives.
Poly(vinylamine) is a linear cationic polymer with minimal branching and it contains one amine functional group for every two carbon units. A partially hydrolyzed poly(vinylamine) may contain primary amine, amide and amidine functionalities. Poly(vinylamine) is typically made by solution, free-radical polymerization of N-vinylformamide monomer, followed by base- or acid-catalyzed hydrolysis. U.S. Pat. No. 4,275,002 disclosed a process of preparing poly(vinylamine) using N-vinylacetamide monomer through free-radical polymerization followed by hydrolysis using a mineral acid. U.S. Pat. No. 4,774,285 described the preparation of copolymer of N-vinylformamide and vinyl alcohol. U.S. Pat. No. 5,630,907 disclosed the copolymer of vinylamine and acrylic acid. U.S. Pat. No. 6,797,785 disclosed the preparation of the copolymers of vinylamine with diallyldimethylammonium chloride and vinylamine with acrylamide via reverse emulsion polymerization, and the uses as flocculants and coagulants for papermaking. EP 0251182 described the use of copolymers of vinylamine and acrylonitrile for papermaking as drainage aids, retention aids, and wet end additives to increase paper strength.
U.S. Patent Application No. 20090314446 described a method of preparing low amidine content poly(vinylamine) and the usage of such polymer to increase papermaking retention and drainage rate and enhance paper dry strength, and other applications.
The amine functionalities, either primary amine or amidine, of poly(vinylamine) can react with a variety of compounds having reactive functional groups. Post-polymerization chemical modification of poly(vinylamine) with a compound having functional groups is an alternative approach to produce poly(vinylamine) derivatives with altered or improved chemical, physical and application properties. U.S. Pat. No. 5,292,441 described the use of quaternized poly(vinylamine)s as flocculants for wastewater clarification, where the quaternized poly(vinylamine) was obtained via the reaction of poly(vinylamine) with an alkylating agent, such as methyl chloride, dimethyl sulfate, or benzyl chloride. U.S. Pat. No. 5,994,449 described a resin composition as a reaction product of epihalohydrin with the mixture of a poly(vinylamine-co-vinyl alcohol) and poly(aminoamide), and the use of the resin as creping adhesives.
More recently, U.S. Pat. No. 7,902,312 disclosed various Michael addition adducts of poly(vinylamine), and the uses of these modified poly(vinylamine) as dry strength additives and/or retention/drainage aids for papermaking. U.S. Patent Application Nos. 20090043051 and 20100193148 described numerous modified poly(vinylamine) products prepared by alkylation, acylation and condensation reactions of the poly(vinylamine) with a variety of amine-reactive compounds. In these two patent applications, the amine groups of vinylamine-containing polymers are substituted with cationic, anionic, hydrophobic and hydrophilic functional groups, or the combination of those functional groups. The uses of those modified poly(vinylamine) products are also described for papermaking as dry strength additives, retention and drainage aids, as well as pitch and stickies control agents in the applications,
As mentioned in the prior art, a poly(vinylamine) derivative can also be prepared using N-vinylacetamide monomer through free-radical solution polymerization followed by hydrolysis of the acetamide functional group to liberate a free amine group on the polymer backbone and release acetic acid. The disadvantage of the prior art is that it requires a monomer that is expensive and commercially unavailable for industrial production. Additionally, poly(N-vinylacetamide) is more stable than poly(N-vinylformamide) in water and thereby more resistant to hydrolysis.
The present invention is directed to a new process of producing acylated poly(vinylamine), particularly acetylated poly(vinylamine), using a readily available acylating agent, e.g., acyl anhydrides, or acyl chlorides, preferably acetic anhydride, propionic anhydride, acetyl chloride and propionyl chloride. Acylation of a poly(vinylamine) by acetic anhydride or propionic anhydride or acetyl chloride can be completed with high reaction efficiency and without by-products except acetic acid, propionic acid or chloride, respectively.